JP6707861B2 - Biaxially oriented polyester film - Google Patents

Description

The present invention relates to a biaxially oriented polyester film having excellent runnability and slitting property, excellent dimensional stability and surface characteristics, for optical and various release films, and next-generation thermal transfer requiring high-definition surface property. The present invention relates to a biaxially oriented polyester film which can be suitably used as a base film of a coating type magnetic recording medium such as a ribbon film and a data storage.

Biaxially oriented polyester films are used in various applications because of their excellent thermal properties, dimensional stability, mechanical properties, and ease of control of surface morphology, and are particularly useful as supports for magnetic recording media. Are known. High density recording is always required for the magnetic recording medium, and in order to achieve higher density recording, it is not possible to make the magnetic layer thin and to improve the smoothness of the magnetic layer surface by using a fine particle magnetic material. It is valid.

In recent years, in magnetic recording medium supports using ferromagnetic hexagonal ferrite powder, the thinning of the magnetic layer, non-magnetic layer and backcoat layer has restricted the roughening of the running surface as well as the smooth surface. ing. When stored in a roll state as a magnetic recording medium in the manufacturing process, the protrusions formed on the running surface are transferred to the magnetic surface to form dents on the smooth magnetic layer surface, or large particles contained in the support. However, there is a problem that the smoothness of the surface of the magnetic layer is deteriorated by the fact that the surface of the magnetic layer is pushed up to the smooth surface and a smooth convex ridge is generated on the surface of the magnetic layer. In order to improve the smoothness of the surface of the magnetic layer, the diameter of the particles contained in the support is reduced to improve the smoothness as an ultra-high-definition surface, so that the running property, winding property, slitting property, and surface durability are improved. Is insufficient.

Therefore, it can be said that a demand for improvement of characteristics such as compatibility of running property, slit property and surface smoothness is always generated for high density recording.

In order to solve the above-mentioned problems, a polyester film (for example, Patent Document 1) in which fine particles are contained to control the roughness of the film surface and the height and number of protrusions to suppress the transfer to the surface of the magnetic layer has been studied. . However, even if a protrusion of a specific height or size formed on the surface of the base film on the back coat layer side is specified, the magnetic layer or the back coat layer is thin and a ferromagnetic hexagonal ferrite powder having a fine surface is used. When it is used as a support for a magnetic recording medium, it is still impossible to reduce coarse protrusions, and it is impossible to eliminate the decrease in smoothness of the magnetic surface due to transfer. Further, since the laminated thickness on the side on which the magnetic layer is not formed is large, the smoothness defect on the magnetic layer side cannot be eliminated by pushing up to the opposite surface (magnetic layer side) by the surface protrusion. Furthermore, as the diameter of the contained particles becomes smaller, the protrusions become lower, so that the protrusions having a height that contributes to the running property decrease, and problems remain in the running property, the winding property, and the surface abrasion resistance. Further, by controlling the waviness of the surface of the polyester film within a specific range, it is possible to achieve both the runnability and smoothness of a polyester film (for example, Patent Documents 2 to 4) and polyester films that have both excellent windability and electromagnetic conversion characteristics. In order to achieve this, a method of applying a primer on both sides or one side of a polyester film has been studied (for example, Patent Document 5). However, when it is used as a support for a magnetic recording medium that uses a ferromagnetic hexagonal ferrite powder that requires a high-definition surface, the magnetic layer surface is pushed up by particles in the support or protrusions on the backcoat layer surface. The smoothness of the surface of the magnetic layer is still insufficient due to the transfer trace to the magnetic recording medium. In addition, the running durability of the primer layer is insufficient, and there is a problem of contamination in the process due to falling of the contained particles.

JP, 2012-153100, A JP2012-153099A JP, 2003-191414, A JP, 2004-299057, A JP 2001-341265 A

The inventors of the present invention have conducted extensive studies to solve the above-mentioned problems, and as a result, in order to suppress the deterioration of the smoothness of the magnetic layer surface due to the transfer to the magnetic surface and the protrusion of the protrusion, the roughness of the running surface and the surface protrusion It was found that the defects on the surface of the magnetic layer cannot always be reduced only by controlling the height and the number. As a result of further studies, the inventors found out that the unevenness was present in the frequency of protrusions, found that there was a correlation between the unevenness and the decrease in the smoothness of the magnetic surface, and arrived at the present invention.

The object of the present invention is to solve the above problems, a biaxially oriented polyester film having excellent winding property, slitting property, and dimensional stability, and having a smooth magnetic layer when used as a magnetic recording medium, and temperature and It is intended to stably provide a biaxially oriented polyester film which is a high-density magnetic recording medium excellent in electromagnetic conversion characteristics with little dropout due to dimensional change due to environmental change of humidity and storage.

The present invention for solving the above-mentioned problems is characterized by the following respective configurations.

(1) In the roughness curve measured by a three-dimensional surface roughness meter on at least one side, the average diameter (P _L ) of the convex portion and the average diameter (V _L ) of the concave portion at the slice level (reference plane) with a height of 0 nm A biaxially oriented polyester film having a ratio (P _L /V _L ) of 0.3 to 1.2 and an area ratio of protrusions on the reference plane of 30 to 51%.

(2) In the roughness curve measured by a three-dimensional surface roughness meter on at least one side, the protrusion density when the slice level is set at an interval of 10 nm from the reference plane satisfies the following relation, (1) Biaxially oriented polyester film.
0.4≦(M60/M10)×100<10
(However, M10 (pieces/mm ² ): protrusion density at a slice level with a height of 10 nm,
M60 (pieces/mm ² ): protrusion density at a slice level with a height of 60 nm).

(3) The biaxially oriented polyester film as described in (1) or (2) above, wherein the convex part on the reference plane has an average diameter (P _L ) of 2 to 25 μm.

(4) The biaxially oriented polyester film as described in any of (1) to (3) above, wherein the average diameter (V _L ) of the recesses on the reference surface is 3 to 35 μm.

(5) The biaxially oriented polyester film as described in any one of (1) to (4) above, which has a protrusion density (M100) of 5 pieces/mm ² or less at a slice level of 100 nm in height.

(6) The biaxially oriented polyester film as described in any of (1) to (5) above, wherein the film has a thickness of 3.5 to 4.5 μm.

(7) The biaxially oriented polyester film according to any one of (1) to (6), which has a humidity expansion coefficient in the width direction of 0 to 6 ppm/% RH.

(8) The biaxially oriented polyester film as described in any of (1) to (7) above, which is used as a base film for a magnetic recording medium of a coating type digital recording system.

The biaxially oriented polyester film of the present invention is a biaxially oriented polyester film excellent in running property, slit property, and dimensional stability, and has a smooth magnetic layer when used as a magnetic recording medium, and changes in environment of temperature and humidity. It is possible to obtain a biaxially oriented polyester film that is a high-density magnetic recording medium with small dimensional changes due to storage and storage, less dropout, and excellent electromagnetic conversion characteristics, and is also suitable for use as optical and various release films. it can.

Hereinafter, the present invention will be described in detail together with the embodiments.
As the polyester used in the present invention, for example, one composed of a polymer having an acid component such as an aromatic dicarboxylic acid, an alicyclic dicarboxylic acid or an aliphatic dicarboxylic acid or a diol component as a constitutional unit (polymerized unit) is used. You can

Examples of the aromatic dicarboxylic acid component include terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid and 4,4′-diphenyldicarboxylic acid. Acid, 4,4'-diphenyl ether dicarboxylic acid, 4,4'-diphenyl sulfone dicarboxylic acid and the like can be used, and among them, terephthalic acid, phthalic acid and 2,6-naphthalenedicarboxylic acid can be preferably used. .. As the alicyclic dicarboxylic acid component, for example, cyclohexanedicarboxylic acid or the like can be used. As the aliphatic dicarboxylic acid component, for example, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, etc. can be used. These acid components may be used alone or in combination of two or more.

Examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1 ,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2′-bis(4′- β-hydroxyethoxyphenyl)propane and the like can be used, and among them, ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, diethylene glycol and the like can be preferably used, and ethylene glycol is particularly preferable. Etc. can be used. These diol components may be used alone or in combination of two or more.

The polyester may be copolymerized with a monofunctional compound such as lauryl alcohol and phenyl isocyanate, or may be trifunctional such as trimellitic acid, pyromellitic acid, glycerol, pentaerythritol, and 2,4-dioxybenzoic acid. The compound or the like may be copolymerized within a range in which the polymer is substantially linear without excessive branching or crosslinking. In addition to the acid component and the diol component, aromatic hydroxycarboxylic acids such as p-hydroxybenzoic acid, m-hydroxybenzoic acid and 2,6-hydroxynaphthoic acid, and p-aminophenol and p-aminobenzoic acid are also included in the present invention. If the amount is small enough not to impair the effect of, the copolymerization can be further performed.

The copolymerization ratio of the polymer can be examined by using the NMR method (nuclear magnetic resonance method) or the microscopic FT-IR method (Fourier transform microscopic infrared spectroscopy).

As the polyester, those having a glass transition temperature of less than 150° C. can be preferably used in order to perform biaxial stretching and to exhibit the effects of the present invention such as dimensional stability. The polyester used in the present invention is preferably polyethylene terephthalate or polyethylene naphthalate (polyethylene-2,6-naphthalate), and may be a copolymer or modified product thereof or a polymer alloy with another thermoplastic resin. .. The polymer alloy referred to here is a high-polymer multi-component system, and may be a block copolymer formed by copolymerization or a polymer blend formed by mixing. Especially as the polyester of the present invention, it is more preferable that the main component is polyethylene terephthalate because a process of increasing the crystallite size and the crystal orientation is easy to apply. Here, the main component means that it is 80% by mass or more in the film composition.

When polyethylene terephthalate is used as the polymer alloy in the present invention, the other thermoplastic resin is preferably a polymer compatible with polyester, more preferably a polyetherimide resin or the like. As the polyetherimide resin, for example, the ones shown below can be used.

However, in the above formula, R ₁ is a divalent aromatic or aliphatic residue having 6 to 30 carbon atoms, R ₂ is a divalent aromatic residue having 6 to 30 carbon atoms, 2 Selected from the group consisting of alkylene groups having 20 carbon atoms, cycloalkylene groups having 2 to 20 carbon atoms, and polydiorganosiloxane groups chain-terminated with alkylene groups having 2 to 8 carbon atoms. Is a divalent organic group.

Examples of R ₁ and R ₂ include aromatic residues represented by the following formula group.

In the present invention, 2,2-bis[4-(2,3-dicarboxyphenoxy)phenyl]propane dianhydride and m-phenylenediamine, or from the viewpoint of affinity with polyester, cost, melt moldability, and the like, or A polymer having a repeating unit represented by the following formula, which is a condensation product with p-phenylenediamine, is preferable.

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Or

In the above formula, n is an integer of 2 or more, preferably 20 to 50.

This polyether imide is available from SABIC Innovative Plastics under the trade name of "Ultem", and is "Ultem (registered trademark) 1000", "Ultem (registered trademark) 1010", "Ultem (registered trademark) 1040". , "Ultem (registered trademark) 5000", "Ultem (registered trademark) 6000" and "Ultem (registered trademark) XH6050" series and "Extem (registered trademark) XH" and "Extem (registered trademark) UH" registered trademark names Etc. are known.

The biaxially oriented polyester film of the present invention preferably has a laminated structure of two or more layers having at least one layer (B layer) containing inert particles having an average particle diameter of 0.050 to 0.50 μm. In this case, the layer B functions as a layer having a running property and is provided as one outermost layer of the film. It is preferable that the other outermost layer has a laminated structure of at least two layers in which a layer having smoothness (A layer) is provided, because the following characteristic aspects of the present invention can be efficiently obtained.

The biaxially oriented polyester film of the present invention has an average diameter of convex portions (P _L ) and an average diameter of concave portions at a slice level (reference plane) with a height of 0 nm in a roughness curve of a three-dimensional surface roughness meter on at least one side. the ratio of the _{(V L) (P L /} V L) is 0.3 to 1.2. It is preferably 0.5 to 1.0. When (P _L /V _L ) is less than the lower limit value, unevenness occurs in the projection frequency, and it becomes easy to form coarse projections and the runnability and the slit property are easily deteriorated. Further, when the film is stored as a film roll, stress due to winding tightness concentrates on the protrusions, transfer to a smooth surface occurs, and when used as a magnetic recording medium, the smoothness of the surface of the magnetic layer decreases and dropout easily occurs. If (P _L /V _L ) exceeds the upper limit, the slit property may be deteriorated or the area ratio of the present invention may not be satisfied. Setting (P _L /V _L ) within a specific range leads to making the frequency of unevenness with respect to the reference surface uniform, and as a result, the concentration of stress generated during winding tightening on the convex portion is concentrated. Has the effect of dispersing. Therefore, when used as a magnetic recording medium, the electromagnetic conversion characteristics tend to be excellent.

In addition, the reference surface is, as described in the measurement conditions described later, after leveling the entire measurement region after measuring the three-dimensional surface roughness, a cutoff is performed using a specified filter to reduce noise. It is a reference position (height 0 nm) determined when a process of removing components such as undulations and shape is performed. The average diameter of the convex portion (P _L ) is a parameter derived from particle analysis (multiple levels) described in the measurement method described later, and is a cut on the convex side when the film surface is cut in the horizontal direction with the reference plane. Is the equivalent circle diameter. The average diameter (P _L ) of the convex portions is a value calculated by dividing the total area of the convex portions by the number of the convex portions, and calculating the equivalent circle diameter (diameter) from the obtained area of each convex portion. The average diameter (V _L ) of the concave portions is the average equivalent circle diameter of the cut side on the concave side when the film surface is cut in the horizontal direction on the reference plane, and the difference between the measured area and the total area of the convex portions is the It is a value calculated as the equivalent circle diameter (diameter) from the area of each piece obtained by dividing by the number.

The biaxially oriented polyester film of the present invention has an area ratio of protrusions of 30 to 51% at a slice level (reference plane) with a height of 0 nm in a roughness curve measured by a three-dimensional surface roughness meter on at least one surface. It is preferably 40 to 50%. If the area ratio of the convex portions is less than 30%, the running property may be reduced, or unevenness may occur in the protrusion frequency, and the slit property may be reduced. Also, when stored as a film roll, stress due to winding tightness concentrates on the convex portion, and push-up and transfer to a smooth surface occur frequently, so dropout increases when magnetic recording medium is used and good electromagnetic conversion characteristics are obtained. It tends to not be obtained. When the area ratio of the convex portions exceeds the upper limit value, the running property is likely to deteriorate.

Incidentally, the area ratio of the convex portion of the present invention is a parameter derived from particle analysis (multiple levels) described in the measurement method described later, when the film surface for the measurement area is cut in the horizontal direction at the reference plane. It is a percentage of the total area of the cut side on the convex side.

The biaxially oriented polyester film of the present invention has a protrusion density (M60) at a slice level of 60 nm in height and a protrusion density (M10) at a slice level of 10 nm in a roughness curve measured by a three-dimensional surface roughness meter on at least one surface. It is preferable that the relation of 0.4≦(M60/M10)×100<10. The value of (M60/M10)×100 is more preferably 0.4 to 5, and still more preferably 0.4 to 3. If the lower limit value is small, it is preferable that the lower limit value leads to suppression of transfer. When the upper limit value is 10 or more, the ratio of protrusions having a height of 60 nm or more with respect to all the protrusions is high, transfer is likely to occur, and defects on the surface of the magnetic layer are insufficiently suppressed, and dropout is likely to occur. By setting the value of the protrusion density ratio (M60/M10)×100 within the above range, it is possible to achieve a high level of both slitting property and defect suppression on the magnetic layer surface, that is, electromagnetic conversion characteristics.

In the roughness curve of at least one surface of the biaxially oriented polyester film of the present invention measured by a three-dimensional surface roughness meter, the protrusion density (M0) at a slice level (reference surface) with a height of 0 nm is 0.1000 to 10,000 pieces/ It is preferably mm ² . More preferably, it is 0.1000 to 0.9 pieces/mm ² . When the protrusion density (M0) is less than 0.1000 pieces/mm ² , the running property and the slit property tend to be deteriorated. If it exceeds 10,000 pieces/mm ² , the protrusions will be too dense and it will be easy to form coarse protrusions.

In the roughness curve of at least one surface of the biaxially oriented polyester film of the present invention measured by a three-dimensional surface roughness meter, the protrusion density (M10) at a slice level of 10 nm in height is from 60,000 to 20,000 pieces/mm ² . Preferably. It is more preferably from 90,000 to 15,000 pieces/mm ² , and even more preferably from 11,000 to 15,000 pieces/mm ² . If the protrusion density (M10) is out of the above range, the slit property may be deteriorated.

The biaxially oriented polyester film of the present invention has an average diameter (P _L ) of protrusions at a slice level (reference plane) of 0 nm in height of 2 to 25 μm in a roughness curve measured by a three-dimensional surface roughness meter on at least one side. Preferably. The thickness is more preferably 3 to 20 μm, further preferably 5 to 15 μm. If the average diameter of the projections at the slice level (reference plane) with a height of 0 nm is larger than 25 μm, the running property and the slit property may deteriorate. It is desirable that the average diameter (P _L ) is small, but if it is less than 2 μm, it may be difficult to obtain a protrusion having a height effective for running property, and the slit property may deteriorate.

The biaxially oriented polyester film of the present invention has an average diameter (V _L ) of recesses at a slice level (reference plane) of 0 nm in height of 3 to 35 μm in a roughness curve measured by a three-dimensional surface roughness meter on at least one side. Preferably. More preferably, it is 5 to 30 μm. When the average diameter (V _L ) of the recesses is less than 3 μm, the area ratio becomes too large, which may deteriorate the running property. On the other hand, when it exceeds 35 μm, the average diameter (P _L ) of the convex portions also becomes large, and the above (P _L /V _L ) and the area ratio cannot be satisfied, and the running property and the slit property tend to deteriorate.

In the roughness curve of at least one surface of the biaxially oriented polyester film of the present invention measured by a three-dimensional surface roughness meter, the projection density (M100) at a slice level of 100 nm in height is preferably 5/mm ² or less. If the protrusion density (M100) is out of the above range, dropout tends to increase when the magnetic recording medium is used.

It is preferable that the characteristic surface is the surface of the B layer because the slit property is improved and the smoothness defect suppressing effect on the surface of the magnetic layer is sufficiently exhibited.

As a method of controlling the above-mentioned characteristic surface, it is possible to control (when applied to the B layer) by the ratio of the laminated thickness of the B layer to the contained particle diameter, or the particle diameter or content of the particles. In particular, it is preferable to contain two or more kinds of particles having different average particles because the above-mentioned characteristic aspects can be efficiently controlled. Furthermore, it is effective to set the MD multi-stage stretching and the TD stretching ratio ((TD stretching 1)/(TD stretching 2)) described in the stretching method described below within a specific range.

As a method of controlling the above (P _L /V _L ) and the area ratio of the convex portions, at least two kinds of particles (L and M) having different average particle diameters are used in combination in the B layer, and the particles (L ) And the content of particles (M), the layer thickness (t) of the B layer, and the ratio (t/d) of the maximum particle diameter (d) of the B layer can be controlled. The particles (L) preferably have an average particle size of 0.2 to 0.5 μm, and the content of the particles is preferably 0.005 to 0.3% by mass. The average particle diameter of the particles (M) is preferably 0.1 to 0.3 μm, and the content of the particles is preferably 0.1 to 1% by mass. At this time, the particles (L) are particles having a larger average particle diameter than the particles (M). The particle size of each particle is preferably selected so that the particle size ratio (L/M) of the particles (L) to the particles (M) is 2 to 5. The compounding ratio (L/M) of the particles (L) and the particles (M) is preferably 0.02 to 1 or less.

As a method for controlling the above-mentioned protrusion density (M100) or protrusion density ratio (M60/M10)×100, it is preferable that the particle diameter of the particles contained does not exceed 0.5 μm, and the maximum particles that can be contained. The particle diameter of (L) is preferably 0.3 to 0.5 μm, and the content of the particles is preferably 0.005 to 0.3% by mass. When the particle diameter of the particles (L) exceeds 0.4 μm, the content thereof is preferably 0.005 to 0.02 mass %, more preferably 0.005 to 0.015 mass %. Furthermore, the average particle diameter of the particles (M) is preferably 0.1 to 0.3 μm, the content of the particles is preferably 0.1 to 1% by mass, and more preferably 0.1 to 1% by mass. It is 0.35% by mass. The ratio (t/d) of the layer thickness (t) of the layer B to the particle diameter (d) of the particles (L) contained in the layer is preferably 1 to 5, more preferably 1.3. It is preferable to set it to -3. When several kinds of particles having different contained particle sizes are used together, or when there is a width in the distribution of particle sizes, the ratio of the particle size (d) of the largest particle (L) to the laminated thickness may be set within the above range. preferable.

The thickness of the biaxially oriented polyester film of the present invention is preferably in the range of 3.5 to 4.5 μm. If the thickness is less than 3.5 μm, the rigidity and the dimensional stability are deteriorated, and the rigidity of the tape is insufficient, so that the electromagnetic conversion characteristics are likely to deteriorate when the magnetic recording medium is used. Further, it becomes difficult to suppress the push-up toward the smooth surface (A surface) side by the B layer surface projection. If the film thickness is larger than 4.5 μm, the tape length per roll of tape becomes short, which makes it difficult to cope with miniaturization and high capacity of the magnetic tape. As a method of adjusting the thickness, by adjusting the discharge amount of the screw during melt extrusion of the polymer during film formation of the biaxially oriented polyester film, the film after biaxial stretching by controlling the thickness of the unstretched film from the die It is possible to adjust the thickness.

The biaxially oriented polyester film of the present invention preferably has a humidity expansion coefficient in the width direction of 0 to 6 ppm/%RH. When the coefficient of humidity expansion is 6 ppm/% RH or less, when used for a magnetic recording medium, deformation due to humidity change does not become large, and deterioration of dimensional stability hardly occurs. A more preferable upper limit is 5.5 ppm/% RH, and a further preferable upper limit is 5 ppm/% RH. The coefficient of humidity expansion is a physical property that is affected by the degree of tension of the molecular chain, and can be controlled by the ratio of TD stretch 1 and TD stretch 2 as will be described later. It can be controlled by the ratio. The larger the ratio of TD stretch 1 to TD stretch 2 (TD1/TD2), the smaller the humidity expansion coefficient. Further, the higher the total TD stretching ratio, the smaller the humidity expansion coefficient.

In addition, in this invention, MD shows the longitudinal direction (longitudinal direction) of a biaxially oriented polyester film, and TD shows the width direction (transverse direction) of a biaxially oriented polyester film.

The biaxially oriented polyester film of the present invention preferably has a Young's modulus in the width direction of 7 GPa or more, and more preferably 7 to 10 GPa from the viewpoint of controlling the humidity expansion coefficient in the width direction. When the Young's modulus in the width direction is within the above range, the dimensional stability tends to be good when used for a magnetic recording medium due to environmental changes during recording/reproduction of the magnetic recording medium. The Young's modulus in the width direction can be controlled by the temperature and magnification of TD stretching 1, 2 described later. In particular, the total TD magnification affects, and the higher the total TD magnification, the higher the TD Young's modulus.

The biaxially oriented polyester film of the present invention more preferably has a Young's modulus in the longitudinal direction of 3.5 to 8 GPa. When the Young's modulus in the longitudinal direction is within the above range, the storage stability due to the tension during storage of the magnetic recording medium becomes better when used for the magnetic recording medium. A more preferable range of Young's modulus in the longitudinal direction is 3.8 to 7.5 GPa, and an even more preferable range is 4 to 7 GPa. The Young's modulus in the longitudinal direction can be controlled by the MD stretching ratio. The higher the MD magnification, the higher the MD Young's modulus.

The particles that are preferably contained in the B layer of the biaxially oriented polyester film of the present invention are not particularly limited, but either inorganic particles or organic particles can be used. It is preferable to use two or more kinds of particles in combination in order to obtain the features of the present invention. Specific types include, for example, clay, mica, titanium oxide, calcium carbonate, wet silica, dry silica, colloidal silica, calcium phosphate, barium sulfate, alumina silicate, kaolin, talc, montmorillonite, alumina, inorganic such as zirconia. Particles, organic acids having acrylic acid, styrene resin, silicone, imide, etc. as constituent components, core-shell type organic particles, etc. can be exemplified, but in order to control the protrusion diameter and protrusion density of the present invention, a single dispersed spherical shape Are particularly preferred.

The center line surface roughness Ra of the surface of the B layer containing the above particles is preferably 3 to 15 nm, and the 10-point average roughness Rz is preferably 60 to 200 nm. More preferably, Ra is 5 to 12 nm and Rz is 70 to 150 nm. When the surface roughness Ra and Rz are less than the lower limit values, the running property and the slit property are likely to be poor, and when the Ra and Rz exceed the upper limit values, a back coat layer is provided on the surface to cause transfer marks. Electromagnetic conversion characteristics tend to deteriorate.

When the biaxially oriented polyester film of the present invention is used as a base film for a magnetic recording medium, it is preferable to provide a back coat layer (hereinafter referred to as BC layer) on the characteristic surface side in order to obtain a high density magnetic recording medium, In particular, a magnetic recording medium using ferromagnetic hexagonal ferrite powder for the magnetic layer has a thin thickness of the magnetic layer, the non-magnetic layer and the BC layer itself. Therefore, when the BC layer is provided on the above-mentioned characteristic surface, the surface of the BC layer is formed. The effects of the protrusions caused by the support are less likely to occur, and an ultra-flat surface can be obtained without forming a transfer mark on the magnetic surface, so that excellent electromagnetic conversion characteristics can be exhibited.

The biaxially oriented polyester film of the present invention as described above is manufactured, for example, as follows.

First, polyester pellets are melted using an extruder, discharged from a die, and then cooled and solidified to form a sheet. At this time, it is preferable to filter the polymer with a fiber-sintered stainless metal filter in order to remove the unmelted material in the polymer.

Various additives, such as compatibilizers, plasticizers, weathering agents, antioxidants, heat stabilizers, lubricants, antistatic agents, brighteners, and colorants, as long as they are within the range that does not impair the features of the present invention. , A conductive agent, a crystal nucleating agent, an ultraviolet absorber, a flame retardant, a flame retardant aid, a pigment, a dye, etc. may be added.

Subsequently, the sheet is biaxially stretched in the longitudinal direction and the width direction, and then heat treated. In order to improve the average diameters (P _L , V _L ) of the convex portions and the concave portions on the reference plane and the dimensional stability in the width direction, the stretching step is particularly divided into two or more stages in the longitudinal direction and two or more stages in the width direction. preferable. That is, in the present application, the stretching ratio in the transverse direction becomes larger than that in the longitudinal direction in order to obtain high dimensional stability in the transverse direction, and as a result, the shape of the protrusions becomes anisotropic, so that the average diameter ratio of the convex portions and the concave portions is increased. It is difficult to obtain (P _L /V _L ). However, when the longitudinal multi-stage stretching is carried out, the crystallinity of the protrusions formed by the stretching is kept low, so that the average diameters (P _L , V _L ) are controlled and the above-mentioned average diameter ratio (P _L /V _L ) is maintained. It is thought that it can be controlled efficiently.

As a stretching method, a sequential biaxial stretching method in which stretching is performed in the longitudinal direction and then in two steps in the width direction, and a stretching method in which simultaneous biaxial stretching is performed and then further stretching in the width direction is preferable.

Hereinafter, the method of producing the film of the present invention will be described by taking an example of using polyethylene terephthalate (PET) as polyester as a typical example. Note that the present application is not limited to the PET film, and one using another polymer may be used. For example, when a polyester film is formed using polyethylene-2,6-naphthalene dicarboxylate having a high glass transition temperature or a high melting point, extrusion or stretching may be performed at a temperature higher than the temperature shown below.

First, PET pellets are manufactured. PET is manufactured by any of the following processes. That is, (1) a process in which terephthalic acid and ethylene glycol are used as raw materials, a low molecular weight PET or oligomer is obtained by a direct esterification reaction, and then a polymer is obtained by a polycondensation reaction using antimony trioxide or a titanium compound as a catalyst. , (2) A process in which dimethyl terephthalate and ethylene glycol are used as raw materials to obtain a low molecular weight compound by a transesterification reaction, and then a polycondensation reaction using an antimony trioxide or titanium compound as a catalyst to obtain a polymer.

In order to incorporate the particles into PET forming the film, it is preferable to disperse the particles in a predetermined ratio in ethylene glycol in the form of a slurry and add the ethylene glycol during the polymerization. When the particles are added, for example, when the particles in the water sol or alcohol sol state obtained during the synthesis of the inert particles are added without being dried, the dispersibility of the particles is good. Further, a method in which a water slurry of inert particles is directly mixed with PET pellets and kneaded into PET using a vent type twin-screw kneading extruder is also effective. As a method of adjusting the content of the inert particles, a master pellet of high-concentration inert particles is prepared by the above method and diluted with PET that does not substantially contain the inert particles during film formation. A method of adjusting the content of active particles is effective. At this time, it is effective to control the above-mentioned protrusion density (M100) by adjusting the intrinsic viscosity of PET containing no particles higher than the intrinsic viscosity of the pellets containing particles.

Next, the obtained PET pellets were dried under reduced pressure at 180° C. for 3 hours or more, and then fed to an extruder heated to 270 to 320° C. under a nitrogen stream or under reduced pressure so that the intrinsic viscosity would not decrease. Then, it is extruded from a slit die and cooled on a casting roll to obtain an unstretched film. At this time, it is preferable to use various filters, for example, filters made of materials such as sintered metal, porous ceramics, sand, and wire mesh in order to remove foreign matters and denatured polymers. Further, it is extremely preferable to provide the gear pump in order to improve the quantitative supply property and obtain the desired t/d in order to form the above-mentioned characteristic surface. To laminate the films, two or more extruders and manifolds or confluence blocks may be used to melt laminate a plurality of different polymers.

Next, the unstretched film thus obtained is stretched in the machine direction using the longitudinal stretching machine in which several rolls are arranged, utilizing the peripheral speed difference of the rolls (MD stretching). A biaxial stretching method in which the transverse stretching is performed in two stages by a stenter (TD stretching 1, TD stretching 2) will be described.

First, the unstretched film is MD stretched. The MD stretching temperature depends on the type of polymer used, but can be determined by using the glass transition temperature (Tg) of the unstretched film as a guide. The temperature is preferably in the range of Tg-10 to Tg+15°C, more preferably Tg°C to Tg+10°C. When the stretching temperature is lower than the above range, film breakage frequently occurs and the productivity is lowered, and it may be difficult to perform stable stretching in two-stage TD stretching after MD stretching. The MD stretching ratio is 3.3 to 6 times, preferably 3.3 to 5.5 times. It is effective to carry out MD stretching in multiple stages of two or more stages in order to control the projection diameter (P _L ). In that case, it is preferable to set the MD stretch ratio of the first stage to 75% or more, preferably 80% or more of the total MD stretch ratio.

Next, TD stretching is performed using a stenter. In order to efficiently control the ratio (P _L /V _L ) of the average diameter (P _L ) of the convex portions and the average diameter (V _L ) of the concave portions of the present invention, two stages in the TD direction in zones of different temperatures are used. It is preferable to stretch. First, the stretching ratio of the first stage stretching (TD stretching 1) is preferably 3.2 to 6.0 times, and more preferably 3.3 to 5.8 times. The stretching temperature of TD stretching 1 is preferably in the range of (cold crystallization temperature of film after MD stretching (hereinafter referred to as Tcc.BF)-5°C) to (Tcc.BF+5°C), and more preferably (Tcc. BF−3° C.) to (Tcc.BF+5° C.).

Next, the second stage stretching (TD stretching 2) is performed in the stenter. The draw ratio of TD stretching 2 is preferably 1.2 to 2 times, more preferably 1.3 to 1.8 times, and further preferably 1.3 to 1.6 times. Setting the TD stretch ratio (TD stretch 1)/(TD stretch 2) in the range of 2 to 3 means that the ratio of the average diameter (P _L ) of the convex portions to the average diameter (V _L ) of the concave portions (P _L ). _L /V _L ) is an effective means for setting it within the above range. The stretching temperature of TD stretching 2 is preferably in the range of (TD stretching 1 temperature +50) to (TD stretching 1 temperature +100)°C, and more preferably (TD stretching 1 temperature +60) to (TD stretching 1 temperature +90)°C. Do in range.

Subsequently, the stretched film is heat-set while being stretched or relaxing in the width direction. As the heat setting treatment condition, the heat setting temperature is preferably 180 to 210°C. The upper limit of the heat setting temperature is more preferably 205°C, further preferably 200°C. The lower limit of the heat setting temperature is more preferably 185°C, further preferably 190°C. The heat setting treatment time is preferably in the range of 0.5 to 10 seconds and the relaxation rate is preferably 0.3 to 2%. After the heat-setting treatment, the gripped clip is released to reduce the tension applied to the film, and the film is rapidly cooled to room temperature. Then, the film edge is removed and the film is wound on a roll to obtain the biaxially oriented polyester film of the present invention. In addition, there is a difference between the stretching temperature of TD stretching 2 and the heat setting temperature, and if the heat setting temperature is higher than the above range, the film tends to relax, and it becomes difficult to obtain the humidity expansion coefficient of the present invention, and the dimensional stability decreases. It's easy to do. If the heat setting temperature is too low, the crystallinity tends to be low, and the flatness of the base film tends to deteriorate in the manufacturing process of the magnetic recording medium, so that the electromagnetic conversion characteristics tend to deteriorate.

Next, the magnetic recording medium is manufactured, for example, as follows.

The magnetic recording medium support (biaxially oriented polyester film) obtained as described above is slit into, for example, a width of 0.1 to 3 m, and conveyed at a speed of 20 to 300 m/min and a tension of 50 to 300 N/m. On the other hand, one surface is coated with a non-magnetic coating material by an extrusion coater to a thickness of 0.5 to 1.5 μm, dried and then coated with a magnetic coating material to a thickness of 0.1 to 0.3 μm. Then, the support coated with the magnetic paint and the non-magnetic paint is magnetically oriented and dried at a temperature of 80 to 130°C. Then, a back coat having a thickness of 0.3 to 0.8 μm is applied to the opposite surface, calendered, and then wound. The calendering process is carried out at a temperature of 70 to 120° C. and a linear pressure of 0.5 to 5 kN/cm using a small test calendering device (metal roll, 7 stages). After that, aging treatment is performed at 60 to 80° C. for 24 to 72 hours, and slitting is performed to a width of 12.65 mm to prepare a pancake. Next, a specific length of this pancake is incorporated into a cassette to obtain a cassette tape type magnetic recording medium.

Here, examples of the composition of the magnetic paint include the following compositions.
Hereinafter, when simply described as “part”, it means “part by mass”.

[Magnetic layer forming coating liquid]
Barium ferrite magnetic powder 100 parts [plate diameter: 20.5 nm, plate thickness: 7.6 nm, plate ratio: 2.7, Hc: 191 kA/m (≈2400 Oe) saturation magnetization: 44 Am ² /kg, BET specific surface area: 60m ² /g]
Polyurethane resin 12 parts Weight average molecular weight 10,000
Sulfonic acid functional group 0.5 meq/g
α-alumina HIT60 (manufactured by Sumitomo Chemical Co., Ltd.) 8 parts Carbon black #55 (manufactured by Asahi Carbon Co., Ltd.) Particle size 0.015 μm 0.5 part Stearic acid 0.5 part Butyl stearate 2 parts Methyl ethyl ketone 180 parts Cyclohexanone 100 parts

[Coating liquid for forming non-magnetic layer]
Non-magnetic powder α Iron oxide 100 parts Average major axis length 0.09 μm, BET specific surface area 50 m ² /g
pH 7
DBP oil absorption 27-38ml/100g
Surface treatment layer Al ₂ O ₃ 8% by mass
Carbon black 25 parts Conductectex SC-U (made by Colombian Carbon Co.)
Vinyl chloride copolymer MR104 (manufactured by Zeon Corporation) 13 parts Polyurethane resin UR8200 (manufactured by Toyobo) 5 parts Phenylphosphonic acid 3.5 parts Butyl stearate 1.0 part

The magnetic recording medium is, for example, for data recording, specifically for computer data backup (for example, linear tape type recording medium (LTO5, LTO6, next-generation LTO tape (LTO7)) and for recording digital images such as video. It can be preferably used for

The magnetic recording medium of the coating type digital recording system in which the biaxially oriented polyester film of the present invention is used is, for example, a magnetic coating liquid in which a ferromagnetic powder such as barium ferrite is uniformly dispersed in a binder such as polyurethane resin. And a magnetic recording medium having a magnetic layer formed by applying the coating liquid.

The biaxially oriented polyester film of the present invention can be used as an optical film, a polarizing plate using the same, and an optical compensation film for a liquid crystal display device. With the recent development of thin and lightweight notebook PCs and thin electronic mobiles, the demand for thinner optical compensation films for liquid crystal display devices has become extremely strict, making them suitable as thin optical films with excellent transparency and runnability. Can be used.

The biaxially oriented polyester film of the present invention can also be used as a release film. The release film is formed by coating a polyester film as a base material with a resin layer having releasability, such as a silicone resin or an epoxy resin. In particular, it is used for various release applications such as production of green sheets, release of liquid crystal polarizing plates, release of liquid crystal protective films, photoresists, and multilayer substrates. Polyester film is generally mixed with an appropriate amount of particles in order to improve processability, such as slipperiness and winding properties, to form fine protrusions on the film surface, but recent refinement of various applications Accordingly, the release film used is also required to have smooth surface properties and runnability without surface defects. Since the biaxially oriented polyester film of the present invention has high-definition surface smoothness and running property, it can be suitably used as a release film for various applications.

(Method of measuring physical properties and method of evaluating effects)
The method of measuring the characteristic value and the method of evaluating the effect in the present invention are as follows.

(1) Average diameter (P _L , V _L ), area ratio of protrusions and protrusion density (M100, M60, M10)
The three-dimensional surface roughness was measured under the following conditions using surf-order ET-4000A manufactured by Kosaka Laboratory, and then particle analysis (multiple levels) was carried out with the built-in analysis software. The measurement conditions are as follows, the slice levels were set at equal intervals of 10 nm, and the average diameter and density of each slice level were measured 5 times at different places, and the average value was taken as the value. The sample set was set on the sample stand so that the X direction of the visual field measurement was the width direction of the biaxially oriented polyester film.

(However, P _L : average diameter of the convex portion at the slice level of 0 nm (reference plane)
V _L : average diameter of recesses at slice level of 0 nm (reference plane)
Area ratio of convex portions: A value obtained by dividing the total area of convex portions at a slice level of 0 nm (reference plane) by the measurement visual field area to obtain a percentage.
M100: Protrusion density at the slice level of 100 nm
M60: protrusion density at a slice level of 60 nm,
M10: Protrusion density at a slice level of 10 nm. )

Equipment: Kosaka Laboratory's "surf-order ET-4000A"
Analysis software: i-Face model TDA31
Stylus tip radius: 0.5 μm
Measurement field of view: X direction: 380 μm Pitch: 1 μm
Y direction: 280 μm Pitch: 5 μm
Needle pressure: 50 μN
Measurement speed: 0.1 mm/s
Cut-off value: Low-0.8mm, High-none Leveling: Full filter: Gaussian filter (2D)
Magnification: 100,000 times Particle analysis (multiple levels) conditions Output content settings: Peak particles (when measuring P _L diameter and protrusion density), valley particles (when measuring V _L diameter)
Hysteresis width: 5 nm
Slice level equal intervals: 10 nm

(2) Surface property of layer B, centerline surface roughness Ra, 10-point average roughness Rz
Using the apparatus described in (1) above, the three-dimensional roughness of the B layer surface was measured 10 times at different locations under the measurement conditions described above, and the average value was measured for the surface roughness Ra and 10-point average roughness, respectively. Rz.
In addition, the surface property was judged according to the following criteria, and C was regarded as poor smoothness.
AA: Rz is 100 nm or less,
A: Rz is more than 100 nm and 150 nm or less,
B: Rz is more than 150 nm and less than 200 nm,
C: Rz is 200 nm or more

(3) Humidity Expansion Coefficient in Width Direction and Dimensional Stability The film is measured in the width direction in the following conditions, and the average value of the results of three measurements is taken as the humidity expansion coefficient in the present invention.
Measuring device: Shimadzu's thermomechanical analyzer TMA-50 (humidity generator: ULVAC-RIKO humidity atmosphere controller HC-1)
Sample size: Film longitudinal direction 10 mm x Film width direction 12.6 mm
Load: 0.5g
Number of measurements: 3 times Measurement temperature: 30°C
Measured humidity: Hold dimensions at 40%RH for 6 hours, measure dimensions, increase humidity to 80%RH in 40 minutes, hold at 80%RH for 6 hours, and then measure the dimensional change ΔL (mm) in the width direction of the support. To do. The humidity expansion coefficient (ppm/%RH) was calculated from the following formula.
Humidity expansion coefficient (ppm/%RH)=106×{(ΔL/12.6)/(80-40)}
The dimensional stability was determined as follows, and C was determined to be poor dimensional stability.
AA: Humidity expansion coefficient is 5.5 ppm/% RH or less A: Humidity expansion coefficient is more than 5.5 ppm/% RH and 6.0 ppm/% RH or less B: Humidity expansion coefficient is more than 6.0 ppm/% RH 6. Less than 5ppm/%RH C: Humidity expansion coefficient is 6.5ppm/%RH or more

(4) Lamination Thickness Under the following conditions, cross-section observation was performed in 10 different fields of view, and the average value of the obtained thickness [nm] was calculated to be the thickness of the A layer [nm].
Measuring device: Transmission electron microscope (TEM) Hitachi H-7100FA measuring condition: Accelerating voltage 100 kV
Measurement magnification: 10,000 times Sample preparation: Ultra thin film section method Observation surface: TD-ZD cross section (TD: width direction, ZD: thickness direction)
Number of measurements: 3 points and 10 fields of view are measured per field of view.

(5) Refractive index It measured using the following measuring device according to JIS-K7142 (2008).
Device: Abbe refractometer 4T (manufactured by Atago Co., Ltd.)
Light source: Sodium D line Measurement temperature: 25°C
Measuring humidity: 65%RH
Mounting solution: methylene iodide (However, when the refractive index is 1.74 or more, sulfur methylene iodide was used.)
Average refractive index n_bar=((nMD+nTD+nZD)/3)
Birefringence Δn=(nMD-nTD)
nMD; Refractive index in film longitudinal direction nTD; Refractive index in film width direction nZD; Refractive index in film thickness direction

(6) Young's modulus The Young's modulus of the film was measured according to ASTM-D882 (1997). An Instron type tensile tester was used and the conditions were as follows. The average value of the results of 5 measurements was defined as the Young's modulus in the present invention.
Measuring device: Instron ultra-precision material testing machine MODEL5848
Sample size:
In the case of Young's modulus measurement in the film width direction, film longitudinal direction 2 mm × film width direction 12.6 mm
(Gripping interval is 8 mm in the film width direction)
When measuring Young's modulus in the longitudinal direction of the film: 2 mm in the width direction of the film x 12.6 mm in the longitudinal direction of the film
(Gripping interval is 8 mm in the longitudinal direction of the film)
Tension rate: 1 mm/min Measuring environment: temperature 23°C, humidity 65%RH
Number of measurements: 5 times.

(7) Total light transmittance, haze Measured using the following measuring device in accordance with JIS-K 7361-1 (1997) and JIS-K 7136 (2000). The transmittance is measured at five points in the longitudinal direction of the central part of the support, and the average value of the measurement results is taken as the total light transmittance and haze in the present invention.
Measuring device: Turbidity meter (NDH-5000) Made by Nippon Denshoku Industries Co., Ltd. Light source: White LED (5V3W)
Measurement environment: temperature 23°C, humidity 65%RH
Number of measurements: 5 times.
The transparency was judged according to the following criteria, and C was regarded as poor transparency.
A: Haze is 1% or less.
B: Haze is more than 1% and less than 2%.
C: Haze is 2% or more.

(8) Average particle size of particles, maximum particle size, average primary particle size of agglomerated particles The cross section of the film is observed with a transmission electron microscope (TEM) at 10,000 times. At this time, when particles of 1 cm or less can be confirmed on the photograph, the TEM observation magnification is changed to 50,000 times for observation. The section thickness of the TEM was set to about 100 nm, 100 fields of view were measured at different locations, and the equivalent circle equivalent diameters of all the dispersed particles photographed were found. The abscissa axis represents the equivalent circle equivalent diameter and the ordinate axis represents the particle equivalent diameter. The number distribution of particles was plotted as the number, and the equivalent circle equivalent diameter of the peak value was taken as the average particle diameter of the particles. Here, if aggregated particles can be confirmed on the photograph observed at 10,000 times, they are not included in the above plot. When two or more kinds of particles having different particle diameters are present in the film, the number distribution of the equivalent circle diameters may be a distribution having two or more peaks. In this case, each peak value is the average particle size of each particle. The particle size of the maximum particle is the particle size of the particle having the maximum particle size in the photograph observed at 10,000 times.
The average primary particle diameter of the agglomerated particles is observed at 200,000 times using the above apparatus. For 100 agglomerated particles, the equivalent circle equivalent diameters of the individual primary particles constituting the agglomerated particles are determined and plotted in the same manner as above, and the equivalent circle equivalent diameter of the peak value is taken as the average primary particle diameter of the agglomerated particles. To do.

(9) Content of particles 1 g of the polymer was put into 200 ml of a 1N-KOH methanol solution and heated under reflux to dissolve the polymer. 200 ml of water was added to the dissolved solution, and then the liquid was subjected to a centrifugal separator to settle particles, and the supernatant was removed. Water was further added to the particles, and washing and centrifugation were repeated twice. The particles thus obtained were dried, and the content of the particles was calculated by weighing the mass.

(10) Runnability Two films in which the A side and the B side of the film are overlapped are placed on a glass plate, and a 200 g weight (contact area 40 cm ² ) is placed on the film. One end (moving direction side) of the lower film was fixed to the glass, and one end (opposite end to the moving direction) of the upper film was fixed to the detector. The static friction coefficient (μs) when the glass plate was moved 5 mm at a speed of 2 mm/sec was obtained from the following formula.
The runnability was determined as follows.
μs=(tension at start)/(load 200g)
A: μs=0.5 or less B: μs=0.5 or more and 0.6 or less C: μs=0.6 or more.

(11) Slitting property When the film was slit into a tape having a width of 12.65 mm, the slit speed was changed and the sharpness of the film edge was visually evaluated by the following method. In addition, C was determined to have a poor slit property.
AA: Can slit even at a speed of 120 m/min without distortion of the edges.
A: Strain is generated at the end at a speed of 100 m/min or more and less than 120 m/min.
B: Distortion occurs at the end at a speed of 80 m/min or more and less than 100 m/min.
C: Wrinkles are generated on the film surface at a speed of less than 80 m/min and the edges are distorted.

(12) Electromagnetic conversion characteristics A film slit to a width of 1 m is conveyed with a tension of 200 N, a magnetic paint and a non-magnetic paint are applied to one surface of a support according to the following, and slit to a width of 12.65 mm to prepare a pancake. To do. Next, a 200 m-long portion of this pancake was incorporated into a cassette to obtain a magnetic tape.

(Hereinafter, "part" means "part by mass".)
Coating liquid for forming magnetic layer Barium ferrite magnetic powder 100 parts (plate diameter: 20.5 nm, plate thickness: 7.6 nm,
Plate ratio: 2.7, Hc: 191 kA/m (≈2400 Oe)
Saturation magnetization: 44 Am ² /kg, BET specific surface area: 60 m ² /g)
Polyurethane resin 12 parts Weight average molecular weight 10,000
Sulfonic acid functional group 0.5 meq/g
α-Alumina HIT60 (Sumitomo Chemical Co., Ltd.) 8 parts Carbon Black #55 (Asahi Carbon Co., Ltd.)
Particle size 0.015 μm 0.5 part Stearic acid 0.5 part Butyl stearate 2 parts Methyl ethyl ketone 180 parts Cyclohexanone 100 parts

Nonmagnetic layer forming coating liquid Nonmagnetic powder α iron oxide 85 parts Average major axis length 0.09 μm, specific surface area by BET method 50 m ² /g
pH 7
DBP oil absorption 27-38ml/100g
Surface treatment layer Al ₂ O ₃ 8% by mass
Carbon black 15 parts "Conductex" (registered trademark) SC-U (manufactured by Columbian Carbon Co.)
Polyurethane resin UR8200 (manufactured by Toyobo Co., Ltd.) 22 parts Phenylphosphonic acid 3 parts Cyclohexanone 140 parts Methyl ethyl ketone 170 parts Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 205 parts Cyclohexanone 135 parts

Each component of each of the above coating solutions was kneaded with a kneader. The coating solution was pumped through a horizontal sand mill containing an amount of 1.0 mmφ zirconia beads filled to 65% of the volume of the dispersion section, and the coating solution was pumped at 2,000 rpm for 120 minutes (substantially staying time in the dispersion section). ), dispersed. To the resulting dispersion, 5.0 parts of polyisocyanate was added to the paint for the non-magnetic layer, 2.5 parts to the paint of the magnetic layer, and 3 parts of methyl ethyl ketone was further added to obtain a filter having an average pore size of 1 μm. It filtered using and prepared the coating liquid for nonmagnetic layer formation and the coating liquid for magnetic layer formation, respectively.

The obtained non-magnetic layer-forming coating liquid was applied and dried on a PET film so that the thickness after drying was 0.8 μm, and then the magnetic layer-forming coating liquid was dried. To 0.07 μm, and while the magnetic layer is still wet, a cobalt magnet with a magnetic force of 6,000 G (600 mT) and a solenoid with a magnetic force of 6,000 G (600 mT) are used to orient and dry it. Let Then, a back coat layer (carbon black average particle size: 17 nm 100 parts, calcium carbonate average particle size: 40 nm 80 parts, α-alumina average particle size: 200 nm 5 parts) was applied to a polyurethane resin so that the thickness after calendering was 0.5 μm. , Dispersed in polyisocyanate). Then, after calendering with a calender at a temperature of 90° C. and a linear pressure of 300 kg/cm (294 kN/m), curing is carried out at 80° C. for 72 hours. Further, a non-woven fabric and a razor blade were attached to a device having a slitting device and a winding device so that the magnetic surface was pressed against the nonwoven fabric, and the surface of the magnetic layer was cleaned by a tape cleaning device to obtain a magnetic tape.

A recording head (MIG, gap 0.15 μm, 1.8T) and a reproducing GMR head were attached to a drum tester, and the output of the magnetic tape obtained above was measured. The relative speed of the head/tape was set to 15 m/sec, a signal with a track density of 16 KTPI and a linear recording density of 400 Kbpi was recorded, and then the ratio of output to noise was used as the electromagnetic conversion characteristic. The result of Example 6 was determined to be 0 dB, and 2.0 dB or more was determined to be A, less than 2.0 to 0 dB was determined to be B, and less than 0 dB was determined to be C. A is desirable, but B is also practically usable.

(13) Dropout The same number of recordings and reproductions as in (12) above were performed, and the number (number) was measured as a dropout when the tape feed length was 0.5 μm or more and the output decreased by 50% or more per 1 m. However, it was judged according to the following criteria. A tape with less than 600 dropouts is desirable as a high capacity data backup tape.
AA: Dropout less than 100 A: Dropout 100 or more and less than 300 B: Dropout 300 or more and less than 600 C: Dropout 600 or more

Embodiments of the present invention will be described based on the following examples. Here, polyethylene terephthalate is referred to as PET, polyethylene naphthalate is referred to as PEN, and polyetherimide is referred to as PEI.

(1-a) Preparation of PET pellets:
194 parts by mass of dimethyl terephthalate and 124 parts by mass of ethylene glycol were charged into a transesterification reactor, and the contents were heated to 140° C. to dissolve them. Then, 0.3 part by mass of magnesium acetate tetrahydrate and 0.05 part by mass of antimony trioxide were added while stirring the contents, and transesterification was carried out while distilling methanol at 140 to 230°C. Next, 0.5 parts by mass of a 5% by mass ethylene glycol solution of trimethyl phosphate (0.025 parts by mass as trimethyl phosphate) and 0.3 parts of a 5% by mass solution of sodium dihydrogen phosphate dihydrate in an ethylene glycol are added. Parts by mass (0.015 parts by mass as sodium dihydrogen phosphate dihydrate) were added.

When the ethylene glycol solution of trimethyl phosphoric acid is added, the temperature of the reaction contents decreases. Therefore, stirring was continued while distilling excess ethylene glycol until the temperature of the reaction contents returned to 230°C. After the temperature of the reaction contents in the transesterification reactor reached 230°C in this way, the reaction contents were transferred to the polymerization device.

After the transition, the reaction system was gradually heated from 230°C to 275°C and the pressure was lowered to 0.1 kPa. The time required to reach the final temperature and the final pressure was 60 minutes. After reaching the final temperature and the final pressure, a reaction was carried out for 2 hours (3 hours after starting the polymerization), and the stirring torque of the polymerization apparatus was a predetermined value (specific values differ depending on the specifications of the polymerization apparatus, but the present polymerization apparatus was used). The value indicated by polyethylene terephthalate having an intrinsic viscosity of 0.55 was defined as a predetermined value. Then, the reaction system was purged with nitrogen and returned to normal pressure to stop the polycondensation reaction, discharged into cold water in a strand form, and immediately cut to obtain PET pellets of polyethylene terephthalate having an intrinsic viscosity of 0.55 (raw material-1).

Using a rotary vacuum polymerization device, the above PET pellets (raw material-1) were subjected to a heat treatment at a temperature of 230°C for a long time under a reduced pressure of 0.1 kPa to carry out solid phase polymerization (raw material-1k). The longer the heat treatment time, the higher the intrinsic viscosity. The treatment time is 1 hour and the intrinsic viscosity is 0.60, and the treatment time is 5 hours and the intrinsic viscosity is 0.70.

(1-b) Preparation of PEN pellets:
To a mixture of 128 parts by mass of dimethyl 2,6-naphthalenedicarboxylate and 60 parts by mass of ethylene glycol, 0.025 parts by mass of manganese acetate/tetrahydrate salt and 0.005 parts by mass of sodium acetate/trihydrate are added, The transesterification reaction was carried out while gradually increasing the temperature from 150°C to 240°C. On the way, when the reaction temperature reached 170° C., 0.024 part by mass of antimony trioxide was added. Further, when the reaction temperature reached 220° C., 0.042 parts by mass (corresponding to 2 mmol %) of 3,5-dicarboxybenzenesulfonic acid tetrabutylphosphonium salt was added. Then, the transesterification reaction was subsequently carried out, and 0.023 parts by mass of trimethylphosphoric acid was added. Next, the reaction product is transferred to a polymerization apparatus, heated to a temperature of 290° C., and subjected to a polycondensation reaction under a high reduced pressure of 30 Pa, and the stirring torque of the polymerization apparatus has a predetermined value (specifically depending on the specifications of the polymerization apparatus). However, the value indicated by polyethylene-2,6-naphthalate having an intrinsic viscosity of 0.6 in the present polymerization device was defined as a predetermined value). Then, the reaction system was purged with nitrogen and returned to normal pressure to stop the polycondensation reaction, discharged into cold water in a strand form, and immediately cut to obtain a PEN pellet (raw material-1b) having an intrinsic viscosity of 0.6.

(2-a) Preparation of PET Pellets Containing Particles:
A vent type twin-screw kneading extruder of the same direction rotation type heated to 280° C., 80 parts by mass of the above PET pellets (raw material-1) and 10% by mass water slurry of crosslinked polystyrene particles having an average particle size of 0.30 μm. 20 parts by mass (2 parts by mass as crosslinked polystyrene particles) are supplied, the vent hole is kept at a reduced pressure of 1 kPa or less to remove water, and 2% by mass of crosslinked polystyrene particles are included to contain particles having an intrinsic viscosity of 0.62. Pellets (raw material-2a) were obtained.

(2-b) Preparation of PET Pellets Containing Particles:
Into the same direction rotation type bent type twin-screw kneading extruder heated to 280° C., 80 parts by mass of the above PET pellets (raw material-1) and 10% by mass water slurry of crosslinked polystyrene particles having an average particle size of 0.45 μm were added. 20 parts by mass (2 parts by mass as crosslinked polystyrene particles) are supplied, the vent hole is kept at a reduced pressure of 1 kPa or less to remove water, and 2% by mass of crosslinked polystyrene particles are included to contain particles having an intrinsic viscosity of 0.62. Pellets (raw material-2b) were obtained.

(2-c) Preparation of PET Pellets Containing Particles:
90 mass parts of the above PET pellets (raw material-1) and 10 mass% aqueous slurry of colloidal silica particles having an average particle diameter of 0.060 μm were added to a vent-type twin-screw kneading extruder of the same direction rotation type heated to 280° C. 10 parts by mass (1 part by mass as colloidal silica particles) are supplied, the vent holes are kept at a reduced pressure of 1 kPa or less to remove water, and particles having an intrinsic viscosity of 0.62 containing 1% by mass of colloidal silica particles are contained. Pellets (raw material-2c) were obtained.

(2-d) Preparation of PET Pellets Containing Particles:
A vent type twin-screw kneading extruder of the same direction rotation type heated to 280° C., 80 parts by mass of the above PET pellets (raw material-1) and a 10% by mass aqueous slurry of colloidal silica particles having an average particle size of 0.10 μm. 20 parts by mass (2 parts by mass as colloidal silica particles) are supplied, the vent holes are kept at a reduced pressure of 1 kPa or less to remove water, and particles having an intrinsic viscosity of 0.62 containing 2% by mass of colloidal silica particles are contained. Pellets (raw material-2d) were obtained.

(2-e) Preparation of PET Pellets Containing Particles:
A vent type twin-screw kneading extruder of the same direction rotation type heated to 280° C., 80 parts by mass of the above PET pellets (raw material-1) and a 10% by mass water slurry of colloidal silica particles having an average particle size of 0.20 μm. 20 parts by mass (2 parts by mass as colloidal silica particles) are supplied, the vent holes are kept at a reduced pressure of 1 kPa or less to remove water, and particles having an intrinsic viscosity of 0.62 containing 2% by mass of colloidal silica particles are contained. Pellets (raw material-2e) were obtained.

(2-f) Preparation of PEN pellets containing particles:
A bent type twin-screw kneading extruder of the same direction rotation type heated to 280° C., 80 parts by mass of the above-mentioned PEN pellets (raw material-1b) and 10% by mass water slurry of crosslinked polystyrene particles having an average particle size of 0.30 μm. 20 parts by mass (2 parts by mass as crosslinked polystyrene particles) are supplied, the vent hole is maintained at a reduced pressure of 1 kPa or less to remove water, and 2% by mass of the crosslinked polystyrene particles are included to contain an intrinsic viscosity of 0.6. Pellets (raw material-2f) were obtained.

(2-g) Preparation of PEN pellets containing particles:
A bent type twin-screw kneading extruder of the same direction rotating type heated to 280° C., 80 parts by mass of the above-mentioned PEN pellets (raw material-1b) and a 10% by mass water slurry of crosslinked polystyrene particles having an average particle size of 0.45 μm. 20 parts by mass (2 parts by mass as crosslinked polystyrene particles) are supplied, the vent hole is maintained at a reduced pressure of 1 kPa or less to remove water, and 2% by mass of the crosslinked polystyrene particles are included to contain an intrinsic viscosity of 0.6. Pellets (raw material-2 g) were obtained.

(2-h) Preparation of PEN pellets containing particles:
90 mass parts of the above-mentioned PEN pellets (raw material-1b) and a 10 mass% water slurry of colloidal silica particles having an average particle diameter of 0.060 μm were added to a vent type twin-screw kneading extruder of the same direction rotation type heated to 280° C. 10 parts by mass (1 part by mass as colloidal silica particles) are supplied, the vent holes are kept at a reduced pressure of 1 kPa or less to remove water, and particles having an intrinsic viscosity of 0.6 containing 1% by mass of colloidal silica particles are contained. Pellets (raw material-2h) were obtained.

(2-i) Preparation of PEN pellets containing particles:
A bent type twin-screw kneading extruder of the same direction rotation type heated to 280° C., 80 parts by mass of the above-mentioned PEN pellets (raw material-1b) and a 10% by mass aqueous slurry of colloidal silica particles having an average particle size of 0.10 μm. 20 parts by mass (2 parts by mass as colloidal silica particles) are supplied, the vent holes are kept at a reduced pressure of 1 kPa or less to remove water, and particles having an intrinsic viscosity of 0.6 containing 2% by mass of colloidal silica particles are contained. Pellets (raw material-2i) were obtained.

(2-j) Preparation of PEN pellets containing particles:
A bent type twin-screw kneading extruder of the same direction rotation type heated to 280° C., 80 parts by mass of the above-mentioned PEN pellets (raw material-1b) and a 10% by mass aqueous slurry of colloidal silica particles having an average particle size of 0.20 μm. 20 parts by mass (2 parts by mass as colloidal silica particles) are supplied, the vent holes are kept at a reduced pressure of 1 kPa or less to remove water, and particles having an intrinsic viscosity of 0.6 containing 2% by mass of colloidal silica particles are contained. Pellets (raw material-2j) were obtained.

(3) Preparation of two-component composition (PET/PEI) pellets:
Vent type twin-screw kneading extruder of the same direction rotation type having three kneading paddle kneading parts heated to a temperature of 280°C (manufactured by Japan Steel Works, screw diameter 30 mm, screw length/screw diameter=45.5) To the above, the PET pellets (raw material-1) obtained by the above method and the pellets of PEI "Ultem (registered trademark)" 1010 manufactured by SABIC Innovative Plastics Co., Ltd. were supplied, and the shear rate was 100 sec ^-1 , and the residence time was 1 minute. Melt extrusion was carried out to obtain a two-component composition pellet containing 50% by mass of PEI. The glass transition temperature of the produced two-component composition pellet was 150°C (raw material-3).

(Example 1)
Using two extruders E1 and E2, the extruder E1, which was heated to 280° C., had 80 parts by mass of PET pellets (raw material-1k), which had been subjected to solid phase polymerization for 4 hours, as an A layer raw material, and had an average grain size. 20 parts by mass of pellets (raw material-2c) containing colloidal silica particles having a diameter of 0.06 μm were dried under reduced pressure at 180° C. for 3 hours and then supplied. Similarly, in the extruder E2 heated to 280° C., 70 parts by mass of the PET pellets (raw material-1k) used in the A layer were used as the raw material of the B layer, and the pellets containing the colloidal silica particles having an average particle diameter of 0.1 μm (raw material- 2d) 25 parts by mass and 5 parts by mass of crosslinked polystyrene particle-containing pellets having an average particle size of 0.30 μm (raw material-2a) were mixed, dried under reduced pressure at 180° C. for 3 hours, and then supplied. In order to stack these two layers, the stacking thickness ratio (A layer:B layer)=8:1 was set in the T-die, and the B layer side was merged so that it was on the cast drum surface side. The laminated unstretched film was produced by closely cooling and solidifying while applying an electric charge.

This laminated unstretched film was stretched 3.5 times in the longitudinal direction at 88° C. in three stages by a roll-type stretching machine. This stretching was carried out by utilizing the difference in peripheral speed between the rolls of two sets at a first stage of 2.7 times, a second stage of 1.23 times and a third stage of 1.05 times.

While holding both ends of the obtained uniaxially stretched film with clips, the uniaxially stretched film was guided to a preheating zone at a temperature of 90°C in a tenter, and continuously in a heating zone at a temperature of 90°C in a width direction (TD direction) perpendicular to the longitudinal direction. Was stretched 3.5 times (TD stretching 1), and then 1.4 times in the width direction in a heating zone at a temperature of 190° C. (TD stretching 2). Subsequently, heat treatment was performed in the heat treatment zone in the tenter at a temperature of 190° C. for 10 seconds, and further relaxation treatment was performed in the width direction of 0.5% at a temperature of 150° C. Then, after uniformly cooling to 25° C., the film edge was removed, and the film was wound on a core to obtain a 4.5 μm-thick biaxially stretched polyester film. The obtained biaxially oriented polyester film had good film-forming stability, and when the physical properties were evaluated, as shown in the table, it had excellent properties when used as a magnetic tape.

In the following, the raw material compositions, film forming conditions, physical properties of the biaxially oriented polyester film, the characteristics of the magnetic tape and the like of each Example and Comparative Example are shown.

(Example 2)
As shown in the table, a biaxially stretched polyester film having a thickness of 4.5 μm was obtained in the same manner as in Example 1 except that the particle concentration used in the layer B was changed.

(Example 3)
As shown in the table, a biaxially stretched polyester film having a thickness of 4.5 μm was obtained in the same manner as in Example 1 except that the particle concentration used in the layer B was changed.

(Example 4)
Using two extruders E1 and E2, the extruder E1, which was heated to 280° C., contained 74 parts by mass of PET pellets (raw material-1k) that had been subjected to solid phase polymerization for 4 hours as a raw material for layer A, 2 components. 6 parts by mass of the composition pellets (raw material-3) and 20 parts by mass of pellets containing the crosslinked polystyrene particles having an average particle diameter of 0.06 μm (raw material-2c) were dried under reduced pressure at 180° C. for 3 hours and then supplied. Similarly, in the extruder E2 heated to 280° C., 73.6 parts by mass of the PET pellets (raw material-1k) used in the A layer as the B layer raw material, 6 parts by weight of the two-component composition pellets (raw material-3) were used. , 20 parts by mass of pellets containing colloidal silica particles having an average particle diameter of 0.2 μm (raw material-2e) and 0.4 parts by mass of pellets containing crosslinked polystyrene particles having an average particle diameter of 0.45 μm (raw material-2b) were mixed, and 180° C. It was vacuum dried for 3 hours and then supplied. In order to stack these two layers, the stacking thickness ratio (A layer:B layer)=6:1 was set in the T-die, and the B layer side was merged so that it was on the cast drum surface side. The laminated unstretched film was produced by closely cooling and solidifying while applying an electric charge.

This laminated unstretched film was stretched 3.5 times in the longitudinal direction in three stages at 90° C. by a roll-type stretching machine. This stretching was carried out at a speed of 2.5 times for the first step, 1.33 times for the second step, and 1.05 times for the third step by utilizing the peripheral speed difference between two pairs of rolls.

While holding both ends of the obtained uniaxially stretched film with clips, the uniaxially stretched film was guided to a preheating zone at a temperature of 95°C in a tenter, and continuously in a heating zone at a temperature of 90°C in a width direction (TD direction) perpendicular to the longitudinal direction. Was stretched 3.5 times (TD stretching 1), and subsequently 1.4 times in the width direction in a heating zone at a temperature of 195° C. (TD stretching 2). Subsequently, heat treatment was performed in the heat treatment zone in the tenter at a temperature of 190° C. for 10 seconds, and further relaxation treatment was performed in the width direction of 0.5% at a temperature of 150° C. Then, after uniformly cooling to 25° C., the film edge was removed, and the film was wound on a core to obtain a 4.2 μm-thick biaxially stretched polyester film. The obtained biaxially oriented polyester film had good film-forming stability, and when the physical properties were evaluated, as shown in the table, it had excellent properties when used as a magnetic tape.

(Example 5)
As shown in the table, a biaxially stretched polyester film having a thickness of 4.2 μm was obtained in the same manner as in Example 4 except that the particle concentration used in the layer B was changed.

(Example 6)
As shown in the table, a biaxially stretched polyester film having a thickness of 4.2 μm was obtained in the same manner as in Example 4 except that the particle concentration used in the layer B was changed.

(Comparative Example 1)
A biaxially stretched polyester film having a thickness of 4.5 μm was obtained in the same manner as in Example 1 except that the particle raw material used for the layer B and the concentration were changed as shown in the table.

(Comparative example 2)
A biaxially stretched polyester film having a thickness of 4.2 μm was obtained in the same manner as in Example 4, except that the particle raw material and the concentration used in the B layer were changed as shown in the table.

(Comparative example 3)
The particle raw material and concentration used for the B layer were changed as shown in the table, and the layer thickness ratio of the A and B layers (A layer:B layer) was changed to 8:1. Longitudinal stretching conditions are 3.5 times in one direction in the longitudinal direction, 3 times in the width direction (TD direction) (TD drawing 1), and then 1 in the width direction in a heating zone at a temperature of 195°C. A biaxially stretched polyester film having a thickness of 4.5 μm was obtained in the same manner as in Example 4 except that the film was stretched 6 times (TD stretched 2).

(Comparative example 4)
A biaxially stretched polyester film having a thickness of 4.5 μm was obtained in the same manner as in Example 4 except that the particle raw material used for the layer B and the concentration thereof were changed as shown in the table.

(Comparative example 5)
A biaxially stretched polyester film having a thickness of 4.2 μm was obtained in the same manner as in Example 4 except that the laminated thickness ratio of the A and B layers (A layer:B layer)=13:1.

(Comparative example 6)
As the layer A raw material, 80 parts by mass of PEN pellets (raw material-1b) and 20 parts by mass of pellets containing colloidal silica particles having an average particle diameter of 0.06 μm (raw material-2h) were vacuum dried at 180° C. for 3 hours and then supplied. Similarly, in the extruder E2 heated to 280° C., 81.5 parts by mass of the PEN pellets (raw material-1b) used in the A layer as the B layer raw material, and the colloidal silica particle-containing pellets with an average particle diameter of 0.1 μm ( 15 parts by mass of raw material-2i) and 3.5 parts by mass of pellets containing crosslinked polystyrene particles having an average particle size of 0.20 μm (raw material-2j) were mixed, dried under reduced pressure at 180° C. for 3 hours, and then supplied. In order to laminate these two layers, the laminate thickness ratio (A layer:B layer)=1:1.9 in the T-die, the B layer side is merged so that it is the cast drum surface side, and the surface temperature is 25° C. By applying an electrostatic charge to the sample, the mixture was cooled and solidified to produce a laminated unstretched film.

This laminated unstretched film was stretched 5 times in the longitudinal direction in one step at 140° C. by a roll stretching machine.

While holding both ends of the obtained uniaxially stretched film with clips, the uniaxially stretched film was guided to a preheating zone at a temperature of 135° C. in a tenter, and stretched 5.3 times in the width direction (TD direction) perpendicular to the longitudinal direction (TD stretching 1). Then, it was further stretched 1.2 times in the width direction in a heating zone at a temperature of 160° C. (TD stretching 2). Subsequently, heat treatment was carried out at a temperature of 210° C. for 4 seconds in a heat treatment zone in the tenter to remove the film edge, and the film was wound on a core to obtain a biaxially stretched polyester film having a thickness of 5 μm.

(Comparative Example 7)
A biaxial layer having a thickness of 4.2 μm was prepared in the same manner as in Comparative Example 6 except that the particle raw material and the concentration used in the B layer were changed as shown in the table and the layer thickness ratio (A layer:B layer)=6:1. A stretched polyester film was obtained.

Claims (6)

A biaxially oriented polyester film having a laminated structure of at least two layers of an A layer and a B layer, each of the A layer and the B layer being the outermost layer, and the surface of the B layer having the following constitution. Oriented polyester film.
In the roughness curve measured by the three-dimensional surface roughness meter of the B layer surface , the average diameter (P _L ) of the convex portions at the slice level (reference plane) with a height of 0 nm is 2 to 25 μm, and the average diameter of the concave portions (V _L ) is 3～35Myuemu, the ratio of the average diameter of the protrusions (average diameter of _{P L)} and recesses _{(V L) (P L /} V L) is 0.3 to 1.2, and the reference Ri area ratio of 30 to 51% der of the projections in the plane, further, that the projection density at the height 100nm slice level (M100) is 10 pieces / mm ² or less. The biaxial orientation according to claim 1, wherein the protrusion density when the slice level is set at an interval of 10 nm from the reference plane satisfies the following relationship in the roughness curve measured by the three-dimensional surface roughness meter of the B layer surface. Polyester film.
0.4≦(M60/M10)×100<10
(However, M10 (pieces/mm ² ): protrusion density at a slice level with a height of 10 nm,
M60 (pieces / mm ^2): the projection density at the height 60nm slice level Projection density at the height 100nm slice level (M100) is 5 / mm ² or less, a biaxially oriented polyester film according to claim 1 or 2. The thickness of the film is 3.5～4.5Myuemu, biaxially oriented polyester film according to any one of claims 1-3. Humidity expansion coefficient in the width direction is 0~6ppm /% RH, biaxially oriented polyester film according to any one of claims 1-4. It is used as a base film for a magnetic recording medium of coating type digital recording system, the biaxially oriented polyester film according to any one of claims 1-5.